Occurrence and Mechanism of Papaver rhoeas ALS Inhibitors Resistance in Poland

Abstract

Herbicide resistance in weeds, including corn poppy (Papaver rhoeas L.), is an increasing problem compromising global crop production. The aims of this study were to evaluate the susceptibility of P. rhoeas populations in Poland to acetolactate synthase (ALS) inhibitors and elucidate their mechanisms of resistance. Between 2017 and 2020, 157 seed samples were collected nationwide and a dose-response study with various ALS-inhibiting herbicides was performed in glasshouses. This revealed 14 resistant populations with R/S ranges of 2.3–1450.2, 9.5–398.5 and 2–2.5 for tribenuron, iodosulfuron and florasulam, respectively. Eight of them were cross-resistant to both tribenuron and iodosulfuron, three and one populations were singly resistant to tribenuron and iodosulfuron, respectively, and one population had reduced susceptibility to florasulam only. In one population, cross-resistance to tribenuron, iodosulfuron and florasulam was identified. The ED50 of many populations susceptible to ALS inhibitors was close to half the recommended dose of the herbicides tested. In seven out of eight resistant P. rhoeas populations analysed, target-site resistance was identified. Six amino acid replacements were found (Ala197, Arg197, His197, Leu197, Ser197 and Thr197). In one population resistant to ALS inhibitors, no mutations in the ALS gene were detected. An efficient anti-resistance strategy is needed to reduce the development of herbicide resistance in P. rhoeas in Poland.

Prevalence, spatial structure and evolution of resistance to acetolactate‐synthase (ALS) inhibitors and 2,4‐D in the major weed Papaver rhoeas (L.) assessed using a massive, country‐wide sampling

“…Leu197 and Ser197 were the most frequent and widespread alleles, while Ala197 was present in a significantly lower number of populations, on par with Leu574 (Table 1). This contrast was also observed within and among previous studies 15,18,19,23–26 . However, when assaying ALS isoforms identical bar the amino‐acid at codon 197, we found that the enzymatic properties of isoform Ala197 were closest to those of the wild‐type ALS isoform, and that its resistance pattern was similar to that of isoform Ser197.…”

“…This contrast was also observed within and among previous studies. 15,18,19,[23][24][25][26] However, when assaying ALS isoforms identical bar the amino-acid at codon 197, we found that the enzymatic properties of isoform Ala197 were closest to those of the wildtype ALS isoform, and that its resistance pattern was similar to that of isoform Ser197. Conversely, the isoforms encoded by the widespread and frequent Leu197 and His197 alleles had a greatly reduced affinity for the ALS substrate and cofactors (Fig.…”

“…Thus, detection of mutations at all ALS codons involved in herbicide resistance in weeds could have been expected in poppy, which is far from being the case: our work firmly established that the vast majority of resistance-endowing ALS alleles having evolved in poppy carry an amino-acid substitution at codon 197, as also observed in previous works. 15,18,19,[23][24][25][26] This strongly suggests that ALS alleles carrying mutations at other codons critical for herbicide sensitivity may impair enzyme activity, incurring a fitness cost that prevents them from increasing in frequency and spreading. Indeed, non-codon-197 mutant alleles were only observed in very low frequencies in one or few populations (Table 1), except allele Leu574.…”

“…In contrast, resistance to ALS inhibitors in poppy is chiefly due to mutant ALS alleles. 15,18,19,[23][24][25][26] Non-ALS-based resistance also exists in this species, 19,24,25,27,28 but is most often associated to mutant ALS alleles. 24,25,29 This makes poppy an excellent candidate for herbicide resistance diagnosis based on massive parallel ALS sequencing, all the more so as a number of studies in the domains of weed science, enzymology or crystallography have pinpointed at least 42 ALS codons with a proven or a possible role in sensitivity to ALS inhibitors.…”

“…Resistance to synthetic auxins is governed by a complex genetic determinism that is only beginning to be elucidated in a few species, 22 and is therefore monitored in poppy using herbicide sensitivity bioassays. In contrast, resistance to ALS inhibitors in poppy is chiefly due to mutant ALS alleles 15,18,19,23–26 . Non‐ALS‐based resistance also exists in this species, 19,24,25,27,28 but is most often associated to mutant ALS alleles 24,25,29 .…”